1. Field of the Invention.
This invention has relation to apparatus for utilizing the changes in shape of piezoelectric material due to changing electrical signals applied to the material to develop a fluid pressure in a fluid flow conduit which varies with the variations in the electrical signal applied to the piezoelectric material.
This invention has initially found its greatest utility where the fluid pressure is a pneumatic pressure, and where the fluid involved is air.
2. Description of the Prior Art.
It is known to develop a variable air pressure for operating a pneumatic linear motor by supplying air from a constant pressure source through a restrictor to a pressure chamber open to the linear motor, and varying the pressure in the chamber by mechanically controlling a pressure relief valve to bleed off air in the chamber. Mechanical means for operating such valving have heretofore proved unduly slow, imprecise, unresponsive to minute changes and/or unacceptably expensive for use in certain applications.
It is a known that certain crystals such as quartz, Rochelle salt, tourmaline, and barium titanate, have piezoelectric properties such that when an electrical field is applied to them, the crystal changes shape. Piezoelectric materials in common use as electromechanical transducers include barium titanate and four variations of lead zirconate-lead titanate ceramics. These ceramics are polycrystalline in nature. Piezoelectric behavior is induced in these ceramic materials by a polarizing treatment.
It is known to join two transverse-expander plates of piezoelectric ceramic material together face-to-face in such a manner that a voltage applied to two electrodes each in contact with an outer face of a different one of the plates will cause the plates to deform in opposite directions, resulting in a bending action. Such piezoelectric elements were developed by Vernitron and are available under the trade name BIMORPH. Such BIMORPH brand plates can be used in series operation by being positioned between silver foil electrodes.
What was lacking before the present invention was a transducer apparatus which could control the operating pressure in a pressure chamber so that it would vary substantially instantaneously with variation in an electrical control signal, and which was responsive to even the minutest variations in the magnitude of that signal.